The present invention relates generally to data storage systems and in particular to migration of data in a data storage system.
The storage needs of present-day applications have widely varying characteristics. For example, in a database facility, a database application might require high-speed storage to store log files (e.g., redo log files), while the storage of database tables might adequately stored in lower-speed storage. A tiered storage system provides storage volumes having different operational characteristics. Tiered storage systems gives the user (or system administrator) access to a range of performance capability and storage capacity to customize the storage needs for an application. Thus, in the database example, log files might be assigned to a storage volume having high-speed access characteristics. The database tables might be assigned for storage in a lower-tiered storage volume. Tiered storage is especially suitable for managing the cost of storage, by providing flexibility in balancing the changing needs between high speed (expensive) storage and lower performance (low cost) storage in an enterprise.
Data migration must be performed occasionally when the storage capacity of a volume is reached. This involves moving data from the original storage volume to a new storage volume. In a tiered storage system, it might be desirable to maintain the relative tier relationship among the storage volumes associated with an application. High capacity storage systems are increasingly in demand. It is not uncommon that a storage system contains hundreds to several thousands of physical storage devices. Managing such large numbers of physical devices in a tiered storage configuration to effect data migration, where there might be dozens to hundreds of devices at each of a number of tier levels can be a daunting task.